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Oil Loss on York YK chiller

Dear Sirs,
I have a York centrifugal chiller in VN that has oil loss problem,
Because currently I won’t be available to reach the jobsite to check the condition myself, so I made the operator to mail me the running record as attached,
The chiller’s model is YKQVQCK35DFGS,
Compressor model YDTL-95DD,
What has happened to this chiller is the oil level in reservoir will keep dropping down to the bottom of sight glass when chiller runs,
and it could take one day long for the oil to slowly return to reservoir when chiller shutdowns,
The operator has replaced the dehydrator, but it seems not the remedy,
From the record, the LOP which represent the pressure in reservoir is 37.1 Psig,
And the Evaporator P is 35.3 Psig, the LOP is 1.8 Psig higher than Evap P, based on this differential, I won’t connect the possible leak on B.P seal to this oil loss problem,
the disappeared oil is not carried to evaporator otherwise it won't recover to reservoir when chiller shutdows, then where has it gone? accumulated in the compressor?
what could the real cause for this faulty condition?
can anybody kindly advise?
Any suggestions will be appreciated.

another question,
For YK chillers,
what will be the correct or proper pressure differential between Evaporator and LOP for good oil return from evaporator and for the oil drops down from compressor? the smaller the better?
I have seen many YK chillers that have 3-4 Psid and also some have only 1 Psid, both catogaries have good oil return,
if the vent line on oil sump can let more gas vented to suction side, then the sump will be in lower pressure, thus facilites the oil return and dropping, am I correct on my inference?

Taicool;
I do not think I have ever heard of a problem such as this nor do many of the other YK guru's.How all this oil can stack up in the gearcase with a 2-2 1/2" hole draining the gearcase to the oil sump is a mystery to me.....Unless of course something is now plugging or restricting the drain from the gearcase to the oil sump...If it were me...I would remove the entire line from the gearcase to the oil sump and take a look in both the line as well as up in the gearcase where a few smaller drain lines feed the drain...That would only require a couple of "O" rings and some refrigerant transfer/removal. Beyond that my friend....you are breaking new ground on this subject...Please keep all of us up to date on what you find on this one.

If your sump pressure is almost 2 psig above your evap. pressure, theres the beginning of your problem. The vent line comes off near the eye of the impeller, which should theoretically be the lowest pressure in the entire system, even lower than your evap. pressure, thus keeping sump below operating pressure of evap. Assuming your LOP transducer is correct, no way you'll be bringing back oil in run cycle. How long has this been occuring? If it persists, the nose seal may be damaged causing oil sump to slightly pressurized.

Gentlemen,
Thanks for your reply,
I have dealed with several chillers that have LOP higher than Evap P,
the diff is high enough to cause oil return problem, in most cases I have a wornout B.P seal, one exception is caused by a pinched O-Ring that seals diffuser plate and gear housing, in those cases, the oil is carried to refrigerant system and held up there in evaporator, but for the current case I encounter, the oil will slowly return to oil sump when chiller shutdown, that phenomenon could Indicate the oil is stacked up in gear housing, it didn’t go to evaporator.
my query to this phenomenon is if the high LOP(no matter what reason for this) will stop the oil return from evaporator through eductor, will it also obstruct the oil drop from gear housing?

Now that I think about it.....I remember the first YK's installed down in Fla. (R-22)had similar problems and Mssr. DD had us install the liquid line to gearcase feed to insure oil return from the compressor during operation. This line is now standard on all YK's. I do also rememnber how DD had this "fix" ready and waiting on us to call about it. I certainly hope that Taicool shares his findings on this on for sure.

We had some Yks installed at a hospital that had a problem that the oil sump pressure was lower(I do not remember the numbers) and would actually draw refrigerant (134) from cooler to oil sump thinning and cooling oil to point it was causing trips when running unloaded. TOGO DD advised that the vanes on this model in the never ending quest for better efficency numbers would close so tightly that would cause back flow into sump. He had us reposition vane linkage so that vanes wouldnt close so tihgt and it worked!

Hello Sargent,
just feel interested in your case,
can you explain it in more detailed to us?
and how did you ajust the vanes to let them not close so tight?
by adjusting the external link's position?
Thanks a lot in advance.

I am collecting some historical records that might be helpful to this YK oil loss problem,
in the past, I do have dealed with some centrifugal oil loss, for those cases I only have paid attention to the bad oil return from evaporator thru eductor,
but ignored the condition of oil return from gear case,
as to the case I currently encountered, both oil return are in malfunction.
what I got in mind so far is for whatever reasons the LOP increases that is significantly higher than evap pressure, not only more oil will be carried to refrigerant system but it could also stack up in gear case when running.
if I thought in the wrong way, then please correct it.
again, thanks for you guys' help.